Halichondrin B is a structurally complex, macrocyclic compound that was originally isolated from the marine sponge Halichondria okadai, and subsequently was found in Axinella sp., Phakellia carteri, and Lissodendoryx sp. Eribulin is a synthetic analog of halichondrin B. The mesylate salt of eribulin (eribulin mesylate, which is marketed under the trade name HALAVEN®) is approved for the treatment of patients with breast cancer who have previously received at least two chemotherapeutic regimens for the treatment of metastatic disease that included an anthracycline and a taxane in either the adjuvant or metastatic setting.